Desu and Da: Noun Sentences, Negatives, and Past

A noun can identify or classify something: 私は学生です. Japanese does not need a verb equivalent to “am” before 学生. Learn the plain and polite endings together, then keep them separate from the endings of verbs and i-adjectives.

Formation and use

です is polite and だ is plain affirmative. In casual conversation, だ may be omitted in some contexts, but it cannot simply replace every です regardless of the preceding word.

For polite negatives use ではありません or the more conversational じゃありません・じゃないです. Plain negative is ではない or じゃない. These are alternatives, so an exercise must specify which form it asks for.

Comparisons and common errors

Past affirmative is でした politely and だった plainly. Past negative includes ではありませんでした, じゃなかったです, and plain ではなかった. Keep the time word consistent with the chosen ending.

Use 学生ですか for a polite yes/no question. A noun statement with です does not mean that something exists at a location: 本があります and 本です answer different questions.

Practise with explanations

Try the 10 questions below, or open the practice set. Check each answer or the whole set, read the explanation, and retry mistakes. First-attempt results are kept separately on this device.

Connected lessons

• Plain and Polite Japanese: Forms, Tense, and Context
• Japanese I-Adjectives: Negative and Past Forms
• Japanese Na-Adjectives: Na, Da, and Conjugation